Agricultural and Food Science in Finland

AGRICULTURAL AND FOOD SCIENCE IN FINLAND

Vol. 1010 (2001):(2001): 231Ð242.

Weed flora in organically grown spring cereals in Finland

Jukka Salonen, Terho Hyvönen and Heikki Jalli MTT Agrifood Research Finland, Plant Production Research, FIN-31600 Jokioinen, e-mail: [email protected]

The weed flora in organically grown spring cereals was investigated in southern and central Finland in 1997Ð1999 with the primary purpose of determining the species composition and the level of weed infestation. Altogether 165 fields were surveyed in the middle of the growing season. A total of 126 weed species were found, of which 42 exceeded the frequency level of 10%. The most frequent weed species were Chenopodium album, Stellaria media, Galeopsis spp. and Viola arvensis. Elymus repens was the most frequent grass species. The average density of weeds was 469 plants mÐ2 (median 395), and the air-dry biomass was 678 kg haÐ1 (median 567) which accounted for 17% of the total biomass of the crop stand. Infestation by Chenopodium album and the perennial species Elymus repens, Cirsium arvense and Sonchus arvensis is of major concern. Weed control strategies should include direct control measures to overcome weed problems related to the conversion period from conventional to organic growing. Key words: weeds, cereals, biodiversity, organic farming

promoted by the ongoing debate about the ad- Introduction verse environmental impact of conventional agriculture. The area of arable land under organic The governments of many European countries management has expanded rapidly, and in 2000 have launched action plans and environmental it covered about 148 000 ha, or 6.7% of the cul- programmes to encourage organic farming and tivated field area (Luomustrategiatyöryhmä sustainable agriculture as a whole. In Finland, 2001). Roughly 5000 farms in Finland are cur- organic farming has been an economically fea- rently engaged in organic production. sible alternative for continuing crop production Studies on weed flora in organic farming have as it has been eligible for substantial subsidies recently been published in the Nordic countries since 1995, the year that Finland became a mem- (Hald 1999, Rydberg and Milberg 2000) and ber of the European Union (Ministry of Agri- elsewhere in Europe (e.g. Moreby et al. 1994, culture and Forestry 1999). This trend has been Albrecht and Mattheis 1998, Becker and Hurle

231 AGRICULTURAL AND FOOD SCIENCE IN FINLAND

Salonen, J. et al. Weed flora in organically grown spring cereals

1998). A common observation is that organic The survey regions were divided into three farming preserves biodiversity since the number zones (Table 1), roughly applying the phyto- of weed species, weed density and the biomass geographical division proposed by Mukula et al. production of weeds are higher than in conven- (1969). In practice, the zones can be character- tionally cropped fields, which are typically treat- ized by a prevalence of spring cereal production ed with herbicides. Moreover, organic farming in the south and an increasing proportion of could obviously promote populations of rare ar- grassland in crop rotation towards the north-east. able weed species, as it has been demonstrated The predominant soil types also differ between (Mahn 1984, Wilson et al. 1990) that the use of the zones, clay soils being typical of southern herbicides and high rates of nitrogen in conven- Finland, sandy soils of eastern Finland and or- tional farming play a key role in the decline of ganic soils of more northerly parts of the coun- weed flora. try. In Finland, Mukula et al. (1969) studied the Seventy-nine farms were visited during a 4- weed flora of spring cereals in the early 1960s, week period starting in mid-July (weeks no. 28/ when the use of herbicides was still minimal. An 29), by which time the spring cereals had reached inventory of weeds in organically cultivated the heading stage. The study farms practised ei- fields was carried out on some 50 farms visited ther crop husbandry without grassland in crop annually in 1984Ð1986 (Mela 1988). At that time, rotation or animal husbandry with pasture in crop organic farming accounted for only 0.05% of rotation. The information on cropping measures Finland’s total arable field area (Luonnonmukai- was obtained by interviewing the farmers. sen viljelyn toimikunta 1984). The number of study fields in the two farm A weed survey of spring cereal fields con- types was fairly evenly represented in all three ducted in 1997Ð1999 (Salonen et al. 2001) stud- zones, contrary to conventional production in ied the botanical composition of spring cereal which animal husbandry was mainly concentrat- fields in both conventional and organic farming. ed in central Finland (Salonen et al. 2001). The present follow-up report focuses on weed The number of spring cereal fields examined infestation and particularly on species diversity was 165, of which 52% were under oats, 23% in organic spring cereal production at a time barley, 16% wheat and 9% mixed cereals. Grass- when organic farming was rapidly expanding in land was relatively common in crop rotation, terms of both farm numbers and field area. The 41% of study fields being undersown for grass- objective was to demonstrate the need and tar- land. The average area of study fields was 3.8 ha get species for weed control. It also provides (range 0.3 haÐ14.6 ha). reference information on species diversity for similar surveys to be conducted in the future. A more detailed analysis of the factors explaining Weed samples weed occurrence and changes in weed floras will be given separately. The occurrence of weeds was assessed from 10 sample quadrats randomly located in each field. Two sample quadrats were placed at a distance of 1Ð3 m from the sown field edge and the other eight in the central area of the field at more than Material and methods 5 m from the edge. Weed density was determined by counting the number of plants or shoots of Study regions, farms and fields grass weeds by species in a rectangular frame measuring 0.1 m2 (25 cm × 40 cm). In four out The weed survey was carried out in 15 regions of ten sample quadrats, weeds and cereals were in southern and central Finland in 1997Ð1999. cut at the soil surface and their biomass was

232 AGRICULTURAL AND FOOD SCIENCE IN FINLAND

Vol. 10 (2001): 231Ð242.

Table 1. Number of fields surveyed, by region and production type.

Number of fields Region Production type Year No. Zone 5 Total no. Animal Crop Municipality husbandry husbandry

1997 Jokioinen 1 1 S 15 13 2 Lammi 2 2 S 19 11 8 1998 Tammela 3 S 9 5 4 Laukaa/Toivakka 4 CE 12 5 7 Kitee 5 CE 9 7 2 Mikkeli 3 6CE16133 Paimio/Tarvasjoki 4 7S 1679 1999 Laihia 8 CW 5 0 5 Nivala 9 CW 10 6 4 Laitila 10 S 13 10 3 Nurmijärvi 11 S 8 5 3 Vieremä 12 CW 9 4 5 Kihniö/Parkano 13 CW 9 4 5 Iitti 14 S 8 0 8 Imatra/Ruokolahti 15 CE 7 1 6 Total 165 91 74 1 incl. Humppila, Jokioinen, Koski Tl, Loimaa municipality, Somero, Ypäjä 2 incl. Hämeenkoski, Kärkölä, Lammi, Mäntsälä, Pukkila 3 incl. Joroinen, Juva, Mikkeli, Mikkeli rural municipality 4 incl. Lieto 5 Key of zone abbreviation: S = South, CE = Central-East, CW = Central-West weighed by species after the samples had been the heading stage. The full scientific names of dried in an air-flow dryer at 40°C. the 42 most frequent weed species are given in The plant species nomenclature follows that Table 2. of Hämet-Ahti et al. (1998), and the BAYER The term frequency refers to the proportion codes of weeds were derived from the BAYER of fields where the species was found. For each AG company (Bayer 1992). Some genera/taxa, field, the total weed density and biomass were e.g. Galeopsis spp. (incl. Galeopsis bifida, summed over the ten sample quadrats, and this Galeopsis speciosa, Galeopsis tetrahit), Lamium figure was used when averages, standard devia- spp. (incl. Lamium album, Lamium amplexi- tions and median values were calculated for the caule, Lamium hybridum, Lamium purpureum) regions, zones and other classifications. The pro- and Trifolium spp. (incl. Trifolium hybridum, portion of the ten most abundant species rela- Trifolium pratense, Trifolium repens), had to be tive to total density and the total biomass were pooled since they could not be identified by spe- calculated by pooling all the data across all fields cies at the small seedling stage. As regards grass by species and then calculating the proportion species, only Elymus repens and Poa annua were of each species. recorded by species if the species had not reached Species diversity was measured by species

233 AGRICULTURAL AND FOOD SCIENCE IN FINLAND

Salonen, J. et al. Weed flora in organically grown spring cereals

Table 2. Frequencies (%) of weed species by region.

Species / Taxon Year / Region 1 1997 1998 1999 Average 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1997Ð99

Achillea millefolium L. 13 11 22 25 33 19 0 0 10 0 13 22 33 25 14 15 Brassica rapa L. ssp. oleifera (DC.) METZG. 13 21 0 17 0 13 0 20 0 62 25 0 22 25 14 16 Capsella bursa-pastoris (L.) MEDIK. 27 53 22 25 67 75 13 40 10 31 13 33 56 50 14 36 Cerastium fontanum BAUMG. 0 0 22 42 56 38 13 0 30 0 0 78 44 0 14 21 Chenopodium album L. 100 95 100 100 89 100 94 100 100 100 100 89 89 100 86 96 Cirsium arvense (L.) SCOP. 47 32 56 25 11 19 63 80 10 0 50 11 11 63 71 34 Elymus repens (L.) GOULD 80 89 89 92 89 88 44 60 80 77 75 78 100 75 100 81 Equisetum arvense L. 33 26 22 42 11 31 50 20 20 15 13 56 22 13 0 27 Erysimum cheiranthoides L. 67 74 89 75 89 88 69 100 100 62 88 100 89 100 100 82 Fallopia convolvulus (L.) Ë. LÖVE 73 63 89 33 44 56 88 80 70 85 88 11 11 63 86 63 Fumaria officinalis L. 47 53 44 42 33 25 44 40 10 31 88 22 0 75 71 41 Galeopsis L. spp. 80 100 89 100 67 94 94 100 100 85 100 100 100 100 100 93 Galium spurium L. a 40 26 67 25 22 19 56 60 0 69 38 33 0 75 43 37 Gnaphalium uliginosum L. 13 37 33 92 67 50 44 0 100 31 13 89 78 13 71 48 Juncus bufonius L. 0 5 11 58 33 25 0 0 40 0 0 0 33 0 14 15 Lamium L. spp. 33 32 33 8 11 19 56 40 0 31 25 0 0 25 43 25 Lapsana communis L. 33 74 78 83 44 88 69 0 0 85 38 0 11 88 100 57 Lathyrus pratensis L. 33 5 11 0 0 6 38 20 10 0 13 11 0 13 14 12 Matricaria matricarioides (LESS.) PORT. 33 42 78 67 78 69 19 0 50 46 0 100 33 63 86 50 Myosotis arvensis (L.) HILL 33 63 56 58 44 94 81 60 30 38 13 89 67 63 100 60 Persicaria hydropiper (L.) SPACH 0 0 56 25 33 31 0 0 0 15 0 0 0 50 43 15 Persicaria lapathifolia (L.) GRAY 47 74 33 58 44 56 25 40 70 31 13 78 89 38 100 53 Persicaria maculosa GRAY 0 0 33 0 0 0 50 0 0 38 63 0 0 38 43 16 Plantago major L. 20 16 33 33 78 69 6 0 40 23 0 89 44 38 57 35 Poa annua L. 0 0 11 8 44 25 0 0 0 15 13 22 11 0 14 10 Polygonum aviculare L. 67 84 56 33 56 75 63 60 80 85 88 89 56 75 71 70 Ranunculus acris L. 27 26 11 42 0 19 0 0 20 8 0 33 78 0 0 19 Ranunculus repens L. 0 37 22 33 78 31 6 0 70 8 13 78 33 13 43 30 Rumex acetosa L. 05 0580060108011780012 Rumex acetosella L. 7 11 33 0 33 19 13 0 20 0 0 33 0 0 14 12 Sagina procumbens L. 00114233190 0000226700 12 Sonchus arvensis L. 53 89 44 67 11 63 63 0 50 54 50 33 22 63 71 54 Spergula arvensis L. 67 89 89 100 78 94 63 60 100 77 75 100 78 75 100 83 Stellaria media (L.) VILL. 100 95 100 83 100 94 100 100 100 100 88 89 89 100 86 95 Taraxacum officinale WEBER in WIGGERS 40 16 56 0 56 19 38 0 10 0 38 67 56 13 71 30 Thlaspi arvense L. 20 58 0 8 11 6 6 40 10 23 13 0 11 75 29 21 Trifolium L. spp. 40 58 33 25 67 50 63 20 20 38 38 44 44 63 29 42 Tripleurospermum inodorum (L.) SCH. BIP. 73 63 89 33 22 50 100 80 90 8 50 78 11 63 43 58 Tussilago farfara L. 7 16 11 33 22 31 31 0 20 15 0 56 0 0 29 19 Veronica serpyllifolia L. 0 0 0 17 11 0 6 0 20 0 0 67 56 0 29 12 Vicia cracca L. 40 47 22 0 11 19 19 20 20 23 50 33 22 25 0 25 Viola arvensis MURRAY b 87 100 100 83 89 100 100 100 60 92 100 100 89 100 100 93 a = incl. G. aparine, b = incl. V. tricolor 1 Key to region numbers: 1 = Jokioinen, 2 = Lammi, 3 = Tammela, 4 = Laukaa/Toivakka, 5 = Kitee, 6 = Mikkeli, 7 = Paimio/Tarvasjoki, 8 = Laihia, 9 = Nivala, 10 = Laitila, 11 = Nurmijärvi, 12 = Vieremä, 13 = Kihniö/Parkano, 14 = Iitti, 15 = Imatra/Ruokolahti.

234 AGRICULTURAL AND FOOD SCIENCE IN FINLAND

Vol. 10 (2001): 231Ð242. richness, heterogeneity and evenness. Both av- Species evenness was measured by Hill’s erage and total numbers of species were calcu- evenness index E2,1 which was calculated as lated for each zone. Since the number of species depends on the sample size and since the number N (Σ p 2)Ð1 2 = i i , where p is the pro- of sampled fields varied from one zone to an- i N1 exp[ÐΣ p ln(p )] other, total species numbers between zones could i i i not be compared. Therefore, the expected portion of species i individuals of the total pop- number of species E(Sn) was calculated for each ulation of a field (Hill 1973, see also Alatalo zone by rarefaction: 1981). The maximum value (1.0) of evenness index is reached when all species are equally 2 N Ð Ni abundant. Data from the ten 0.1 m sample quad- S ( n ) rats were pooled before the calculation of heter- E(Sn)=Σ 1Ð , i =1 N ogeneity and evenness indices. ()( n ) The material and methods are described in greater detail by Salonen et al. (2001). where E(Sn) = expected number of species in a random sample of n individuals, S = total number of species in the entire collection, Ni = number of individuals in species i, N = total number of Results individuals in the collection, n = sample size (number of individuals) chosen for standardiza- Species diversity tion (see Heck et al. 1975, Krebs 1995). In rarefaction, the numbers of species of larger sam- Altogether 126 weed species were found in samples are scaled down to the given number of in- ple quadrats. The occurrence of the 42 most fre- dividuals which permits the comparison of spe- quent weed species found in more than 10% of cies numbers between samples differing in size. surveyed fields is presented by region (Table 2). We scaled sample sizes down to 5000, 7500, The average number of weed species per field 10 000, 12 500 and 15 000 individuals (the low- was 20 when Galeopsis and Lamium species est number of individuals was 19 152), and cal- were pooled as one species (Table 3); without culated 95% confidence limits for each sample pooling, the number would have been 24 (Salo- size. nen et al. 2001). In comparison, the average Species heterogeneity was measured by the number of weed species in unsprayed conven- Shannon diversity index H’ which was calculat- tional fields was 25.

S Seven weed species were found in more than 80% of surveyed fields: Chenopodium album, ed as ÐΣ pi ln(pi), where s is the number of spe- i =1 Stellaria media, Galeopsis spp., Viola arvensis, Spergula arvensis, Erysimum cheiranthoides and cies in a field and pi the proportion of species i individuals of the total population of a field (see Elymus repens. Seventeen species were found Krebs 1995). If two communities have an equal only in organically cultivated fields. These in- number of species but the relative abundances cluded Bidens radiata, Festuca ovina, Mentha are more even in the first community it has a spp., Vicia hirsuta and V. sativa. On the other higher heterogeneity, i.e., it is more diverse. If hand, the species pool of conventional fields two communities have an equal evenness of rel- included 27 species which were found only in ative abundances of species but the species conventional fields. These included Deschamp- number is higher in the first community it has a sia caespitosa, Alopecurus myosuroides, Poa higher heterogeneity, i.e., it is more diverse (see trivialis, Euphorbia helioscopia and Atriplex pat- Krebs 1995). ula.

235 AGRICULTURAL AND FOOD SCIENCE IN FINLAND

Salonen, J. et al. Weed flora in organically grown spring cereals

Table 3. Total and average number of species, average values of Shannon diversity index (H’) and Hill’s

evenness index (E2, 1) in the whole data and in the three zones (S = South, CE = Central-East, CW = Central- West). Standard deviations are shown in parentheses.

Variable Total Zone SCECW

Total no. of species 126 97 95 74 Average no. of species 19.6 (4.8) 18.5 (4.4) 21.8 (4.6) 19.7 (5.1) H’ 02.04 (0.34) 1.99 (0.33) 2.2 (0.26) 001.93 (0.4)

E2, 1 0.67 (0.1) 0.67 (0.1) 0.68 (0.1) 110.67 (0.1)

Species diversity was highest in the central- proportion of species common to both the south- eastern (CE) zone (Table 3), where both the av- ern and the central-eastern zones was 61.3%. The erage number of species per field and the values values of the evenness index did not differ be- of the Shannon diversity index were highest. tween the zones. Furthermore, the total number of species reached almost the same figure as in the southern (S) zone, even though the number of sampled fields Weed density and biomass production was half of that in the southern zone (88 vs. 44). The rarefaction analysis revealed that species Over all studied fields, the average density of richness was significantly lower in the central- weeds was 469 plants mÐ2 (SD = 340, median = western (CW) zone than in other zones (Fig. 1). 395). Weed density was lowest in the southern The central-eastern and southern zones did not, and highest in the central-western zone (Fig. 2). however, differ in species richness (Fig. 1). The On the animal husbandry farms, the average

Fig. 1. Rarefied species numbers for each zone. The vertical lines show 95% confidence limits.

236 AGRICULTURAL AND FOOD SCIENCE IN FINLAND

Vol. 10 (2001): 231Ð242. weed density was lower than the grand average, namely 409 plants mÐ2 (SD = 311, median = 345) and on crop husbandry farms it exceeded the grand average, namely 543 plants mÐ2 (SD = 361, median = 466). The five most abundant weed species were Chenopodium album (on average 91 plants mÐ2; median = 39), Elymus repens (49 ; 17), Spergu- la arvensis (49 ; 15), Stellaria media (49 ; 24) and Viola arvensis (31 ; 14). There were no sig- nificant differences in infestation by the most abundant species between the farm types, except that the density and biomass of S. arvensis were twice as high on crop husbandry as on animal husbandry farms. Differences in species composition were de- tected between the zones (Fig. 3). As regards weed density, Chenopodium album and Spergu- la arvensis were among the three most abundant species in every zone. Stellaria media was one Fig. 2. Density of weeds by zone. The square in the box of the most abundant species in the southern zone denotes the mean of the data, and the horizontal lines the whereas Elymus repens was the most abundant 25th, 50th and 75th percentile values. The error bars de- species in the central-eastern zone and the third note the 5th and 95th, the crosses the 1st and 99th and the dashes the 0th and 100th percentile values. most abundant in the central-western zone. Gnaphalium uliginosum was another species that was more abundant in eastern and western Fin- land than in the south. A characteristic species duction was highest (median = 955 kg haÐ1) in of eastern Finland was Lapsana communis. organic soils, intermediate (median = 635) in The average biomass production of weeds coarse mineral soils and lowest in clay soils was 678 kg haÐ1 (SD = 547, median = 567). As (median = 473). with weed density, biomass production was low- On animal husbandry farms, the average est in the southern and highest in the central- biomass of weeds was 634 kg haÐ1 (SD = 558, western zone (Fig. 4). Furthermore, biomass pro- median = 495) and on crop husbandry farms

Fig. 3. The ten most abundant species as a proportion of total density in all fields surveyed and in each zone. The Bayer codes for weed species: CHEAL = Chenopodium album, AGRRE = Elymus repens, STEME = Stellaria media, SPRAR = Spergula arvensis, VIOSS = Vio- la spp., GAESS = Galeopsis spp., GNAUL = Gnaphalium uliginosum, ERYCH = Erysimum cheiranthoides, LAPCO = Lapsana communis and POLCO = Fallopia convolvulus.

237 AGRICULTURAL AND FOOD SCIENCE IN FINLAND

Salonen, J. et al. Weed flora in organically grown spring cereals

The most abundant grass species, Elymus repens, was the most efficient biomass producer, as it accounted for 26% of the total weed biomass production pooled over all study fields (Fig. 5). E. repens was abundant in central Finland, particularly in the central-eastern zone. Its average biomass production in the central-eastern and central-western zones was more than double that in the southern zone. This was clearly due to the dominance of soil types, as in clay soils, which are common in the south, the biomass production of E. repens was fairly low (median = 11 kg haÐ1) whereas in coarse mineral soils and organic soils, which are more common in central Fin- land, it was considerably higher (median = 96 kg haÐ1 and 118 kg haÐ1, respectively). In all, the average proportion of weed biomass relative to total vegetative biomass (crop + weeds) was 17%. The perennial weed species Fig. 4. Biomass of weeds by zone. The square in the box Sonchus arvensis and Cirsium arvense were denotes the mean of the data, and the horizontal lines the highly productive. S. arvensis was common in 25th, 50th and 75th percentile values. The error bars de- coarse mineral soils in central-eastern Finland note the 5th and 95th, the crosses the 1st and 99th and the dashes the 0th and 100th percentile values. (see also Fig. 5), its average biomass in infested fields being 131 kg haÐ1. In contrast, C. arvense produced the highest average biomass, 731 kg haÐ1 (SD = 533, median = 619). The five 106 kg haÐ1, in infested clay soils in the south- weed species that produced the highest amounts ern zone. of biomass were Elymus repens (average 178 kg To supplement the findings of the most com- haÐ1; median 53), Chenopodium album (140 ; 23), mon perennial weed species in sample quadrats, Spergula arvensis (53 ; 8), Galeopsis spp. (47 ; we asked farmers to rank the infestation level of 13) and Stellaria media (37 ; 10). these species in their fields (Table 4). In their Broad-leaved species accounted for 72% of opinion, Elymus repens was both the most abun- the average total biomass production of weeds. dant and the most troublesome species.

Fig. 5. The ten most abundant species as a proportion of total biomass in all fields surveyed and in each zone. The Bayer codes for weed species: AGRRE = Elymus repens, CHEAL = Chenopodium album, SPRAR = Spergula arvensis, GAESS = Galeopsis spp., STEME = Stellaria media, SONAR = Son- chus arvensis, CIRAR = Cirsium arvense, POLLA = Persicaria lapathifolia, ERYCH = Erysimum cheiranthoides and LAPCO = Lapsana communis.

238 AGRICULTURAL AND FOOD SCIENCE IN FINLAND

Vol. 10 (2001): 231Ð242.

Table 4. Infestation of survey fields by Elymus repens as in the mid-1980s their proportion ranged from (AGRRE), Cirsium arvense (CIRAR) and Sonchus arven- 10% to 13%, depending on the cereal species sis (SONAR) in the opinion of farmers. (Mela 1988). The median weed density in organ- Infestation level Proportion (%) of fields, by species ic production was only slightly higher (395 plants mÐ2 vs. 374) and the biomass production AGRRE CIRAR SONAR somewhat higher (567 kg haÐ1 vs. 413) than in Negligible 18 46 42 conventional fields not sprayed with herbicides Moderate 67 49 52 (Salonen et al. 2001). Abundant 15 5 6 Most of the fields examined had only a short history of organic farming, the majority of study farms having converted from conventional to organic cropping during the 1990s. A high infestation level such as was observed here is typ- Discussion ical of the early stages of conversion to organic growing (Davies et al. 1997, Albrecht and Som- The total number of weed species (126) found mer 1998). in organically cultivated fields was lower than Chenopodium album was the most harmful the number of species (160) found in the whole broad-leaved species in terms of crop-weed com- survey data, which included 525 conventional petition and weed biomass production. This is in fields (Salonen et al. 2001). In comparison, in agreement with the findings of a weed survey the mid-1980s Mela (1988) found 120 weed spe- conducted in Scotland (Davies et al. 1997), where cies/taxa in organically cultivated cereal fields, C. album, Polygonum aviculare and Spergula and in the early 1960s Mukula et al. (1969) found arvensis were amongst the weed species that ben- 304 species in conventional spring cereal fields efited most from the period of conversion to or- not treated with herbicides. In all surveys, the ganic farming. Hallgren (1996) has reported that lists of most frequent species were very similar C. album decreased in frequency in the 1960s and to each other. 1970s but later, in the 1990s, became more fre- Only one third, namely 42 weed species/taxa quent in conventionally farmed fields in Sweden. out of 126 observed species, exceeded the over- Three perennial weed species, Elymus repens, all frequency level of 10%. None of the observed Cirsium arvense and Sonchus arvensis, proved species is classified as endangered in Finland to be highly competitive and are of major con- (Rassi et al. 2000). Chenopodium album, Galeop- cern in terms of yield reductions. In contrast, sis spp. and Stellaria media are characteristic these perennial species were not particularly species of spring cereal fields in this country common in a recent survey of organic farms in since they have been among the most frequent Sweden, where Rydberg and Milberg (2000) sug- species in all weed surveys (Mukula et al. 1969, gested that improved soil cultivation technology Erviö and Salonen 1987, Mela 1988, Salonen et has reduced the importance of perennial species. al. 2001). Moreover, they seem to be particular- Differences between regions were found in ly typical of organic production, as they exceed- the species diversity, composition and biomass ed the frequency level of 90% in all three zones. production of some species. While the predomi- The level of weed infestation was almost nance of certain soil types in different parts of identical to that in organic production in the mid- Finland was clearly a key factor affecting spe- 1980s (Mela 1988), when the average weed den- cies abundance, the higher species diversity in sity was 505 plants mÐ2 and biomass production eastern Finland was probably due to the greater 575 kg haÐ1. The relative importance of weeds diversity of crop rotations and the less intensive has increased slightly, as they currently account- use of herbicides before conversion to organic ed for 17% of the biomass in crop stands where- farming in that part of the country than else-

239 AGRICULTURAL AND FOOD SCIENCE IN FINLAND

Salonen, J. et al. Weed flora in organically grown spring cereals where. However, the composition of weed flo- Organic farming appears to promote biodiver- ras is a result not of any single factor but of many sity since the number of weed species is often confounding environmental and management higher than in conventional farming (e.g. More- factors (Haas and Streibig 1982, Salonen 1993). by et al. 1994, Hald 1999, Salonen et al. 2001). Therefore, comparisons of zones, farming types However, in the present survey the average etc. should be interpreted with caution. number of weed species per field and the infes- Organic crop production aims to maintain tation level of weeds were about the same both weeds at a manageable level by cultural means in organic fields and in conventional fields not (Bond and Lennartsson 1999). Weed manage- treated with herbicides (Salonen et al. 2001). ment strategies should include crop rotation, Thus, the challenge for both cropping systems is cultivations, crop density, cultivar selection and to find an acceptable balance between profitable mechanical control (Stopes and Millington 1991, and sustainable crop production and the function- Lee 1995, Welsh et al. 1999). Current direct weed al value of a rich weed flora in the arable habitat. control methods alone are often insufficient to control weeds effectively in spring cereal pro- Acknowledgements. The weed survey was a part of the Finn- duction. In fact, only a few of the survey farms ish Biodiversity Programme’s (FIBRE) project “Biodiver- carried out direct weed control measures even sity in agricultural environments“ coordinated by Dr. Juha though these might provide at least moderate Tiainen. We thank farmers who allowed us to visit their control against some species, e.g. C. album. fields and provided us with information about farming prac- tices. The survey was financed by MTT Agrifood Research Moreover, perennial weed species such as Ely- Finland and the Ministry of Agriculture and Forestry. The mus repens, Sonchus arvensis and Cirsium ar- authors acknowledge the pioneer research work and edu- vense will threaten the future of organic cereal cation activities of professor emeritus Eero Varis in the area production unless their control is given due con- of organic crop production. sideration in crop rotation.

References

Alatalo, R.V. 1981. Problems in the measurement of even- Davies, D.H.K., Christal, A., Talbot, M., Lawson, H.M. & ness in ecology. Oikos 37: 199Ð204. Wright, G. 1997. Changes in weed populations in the Albrecht, H. & Mattheis, A. 1998. The effects of organic conversion of two arable farms to organic farming. and integrated farming on rare arable weeds on the Proceedings 1997 Brighton crop protection confer- Forschungsverbund Agrarökosysteme München ence Ð weeds. The British Crop Protection Council. (FAM) research station in southern Bavaria. Biologi- p. 973Ð978. cal Conservation 86: 347Ð356. Erviö, L.-R. & Salonen, J. 1987. Changes in the weed Ð & Sommer, H. 1998. Development of the arable weed population of spring cereals in Finland. Annales Ag- seed bank after the change from conventional to in- riculturae Fenniae 26: 210Ð226. tegrated and organic farming. In: Weed seedbanks: Haas, H. & Streibig, J.C. 1982. Changing patterns of weed determination, dynamics and manipulation. Aspects distribution as a result of herbicide use and other of Applied Biology 51: 279Ð288. agronomic factors. In: LeBaron, H.M. & Gressel, J. Bayer 1992. Important crops of the world and their weeds. (eds.). Herbicide resistance in plants. J. Wiley & Sons. 2nd ed. BAYER AG, Leverkusen. 1682 p. p. 57Ð79. Becker, B. & Hurle, K. 1998. Unkrautflora auf Feldern mit Hald, A.B. 1999. Weed vegetation (wild flora) of long es- unterschiedlich langer ökologischer Bewirtschaftung. tablished organic versus conventional cereal fields Zeitschrift für Pflanzenkrankheiten und Pflanzen- in Denmark. Annals of Applied Biology 14: 307Ð314. schutz, Sonderheft 16: 155Ð161. Hallgren, E. 1996. Do the weed flora and effect of a her- Bond, W. & Lennartsson, M.E.K. 1999. Organic weed bicide change with time. Proceedings Second Inter- control Ð back to the future. Proceedings 1999 Bright- national Weed Control Congress, Copenhagen. on crop protection conference Ð weeds. The British p. 1355Ð1360. Crop Protection Council. p. 929Ð938. Hämet-Ahti, L., Suominen, J., Ulvinen, T. & Uotila, P.

240 AGRICULTURAL AND FOOD SCIENCE IN FINLAND

Vol. 10 (2001): 231Ð242.

(eds.). 1998. Retkeilykasvio (Field Flora of Finland), winter wheat in southern England. Annals of applied 4. ed. Finnish Museum of Natural History, Botanical Biology 125: 13Ð27. Museum. Helsinki. 656 p. Mukula, J., Raatikainen, M., Lallukka, R. & Raatikainen, T. Heck, K.L.J., van Belle, G. & Simberloff, D. 1975. Explicit 1969. Composition of weed flora in spring cereals in calculation of the rarefaction diversity measurement Finland. Annales Agriculturae Fenniae 8: 59Ð109. and the determination of sufficient sample size. Ecol- Rassi, P., Alanen, A., Kanerva, T. & Mannerkoski, I. (eds.). ogy 56: 1459Ð1461. 2000. The 2000 Red List of Finnish species. The Min- Hill, M.O. 1973. Diversity and evenness: a unifying nota- istry of the Environment, Helsinki, 432 p. The II Com- tion and its consequences. Ecology 54: 427Ð432. mittee for the Monitoring of Threatened Species in Krebs, C.J. 1999. Ecological Methodology. Second Edi- Finland, pre-print. http://www.vyh.fi/eng/environ/ tion. Benjamin/Cummins, California. 620 p. naturcon/threat/2000/2000.htm, 24.10.2000. Lee, H.C. 1995. Non-chemical weed control in cereals. Rydberg, N.T. & Milberg, P. 2000. A survey of weeds in Proceedings 1995 Brighton Crop Protection Confer- organic farming in Sweden. Biological Agriculture and ence Ð Weeds. The British Crop Protection Council. Horticulture 18: 175Ð185. p. 1161Ð1170. Salonen, J. 1993. Weed infestation and factors affecting Luomustrategiatyöryhmä 2001. Ehdotus luonnonmukai- weed incidence in spring cereals in Finland Ð a mul- sen elintarviketuotannon kehittämisestä. Maa- ja tivariate approach. Agricultural Science in Finland 2: metsätalousministeriön työryhmämietintö. 17 p. 525Ð536. Luonnonmukaisen viljelyn toimikunta 1984. Luonnonmu- Ð, Hyvönen, T. & Jalli, H. 2001. Weeds in spring cereal kaisen viljelyn toimikunnan mietintö. Komiteanmie- fields in Finland Ð a third survey. Agricultural and Food tintö 1984: 28. 108 p. Science in Finland (in print). Mahn, E.G. 1988. Changes in the structure of weed com- Stopes, C. & Millington, S. 1991. Weed control in organic munities affected by agrochemicals Ð what role does farming systems. Proceedings 1991 Brighton Crop nitrogen play ? Ecological Bulletins 39: 71Ð73. Protection Conference Ð Weeds. The British Crop Mela, T. 1988. Luonnonmukainen viljely Suomessa. Vilje- Protection Council. p. 185Ð192. lymenetelmät, rikkakasvit, peltojen viljavuus, sadot Welsh, J.P., Phillips, L., Bulson, H.A.J. & Wolfe, M. 1999. ja sadon laatu. Summary: Organic farming in Finland. Weed control strategies for organic cereal crops. Pro- Cultivation methods, weeds, soil fertility, yields and ceedings 1999 Brighton Crop Protection Conference yield quality. Helsingin yliopiston kasvinviljelytieteen Ð Weeds. The British Crop Protection Council. p. 945Ð laitoksen julkaisuja no. 16. 220 p. 950. Ministry of Agriculture and Forestry 1999. Agriculture in Wilson, P.J., Boatman, N.D. & Edwards, P.J. 1990. Strat- Finland. 35 p. egies for the conservation of endangered arable Moreby, S.J., Aebischer, N.J., Souhway, S.E. & Sother- weeds in Great Britain. In: Proceedings EWRS Sym- ton, N.W. 1994. A comparison of the flora and ar- posium on Integrated Weed Management in Cere- thropod fauna of organically and conventionally grown als, Helsinki. p. 93Ð101.

241 AGRICULTURAL AND FOOD SCIENCE IN FINLAND

Salonen, J. et al. Weed flora in organically grown spring cereals SELOSTUS Luomukevätviljapeltojen rikkakasvillisuus 1997–1999

Jukka Salonen, Terho Hyvönen ja Heikki Jalli MTT (Maa- ja elintarviketalouden tutkimuskeskus)

Luonnonmukaisesti viljeltyjen kevätviljapeltojen rik- Rikkakasveja kasvoi keskimäärin 469 kpl/m2, ja kakasvillisuutta kartoitettiin Etelä- ja Keski-Suomes- niiden tuottama biomassa oli 678 kg/ha. Rikkakas- sa vuosina 1997Ð1999 yhteensä 15 tutkimusalueella. vien osuus kevätviljapellon kasvimassasta (vilja + Aineistoa kerättiin yhteensä 79 tilalta ja 165 pellol- rikkakasvit) oli 17 %. Juolavehnä oli eniten biomas- ta, joista 52 % oli kauraa, 23 % ohraa, 16 % kevät- saa tuottava laji. Jauhosavikka oli runsain leveäleh- vehnää ja 9 % viljaseosta. Pelloista 41 % oli kylvet- tinen laji. ty suojaviljaksi. Kasvustonäytteet kerättiin kymme- Luonnonmukaista viljantuotantoa uhkaavat erityi- neltä 0,1 m2 näytealalta heinäkuun puolivälin ja elo- sesti kestorikkakasvit juolavehnä, peltovalvatti ja pel- kuun alkupuolen välisenä aikana. to-ohdake. Juolavehnää ja peltovalvattia kasvoi run- Näytealoilta havaittiin yhteensä 126 rikkakasvi- saimmin Itä- ja Kaakkois-Suomessa, pelto-ohdaket- lajia, joista valtaosa oli leveälehtisiä lajeja. Keski- ta puolestaan Etelä-Suomen savialueilla. määräinen lajimäärä oli 20 lajia/sukua peltoa kohti. Useimmat tutkimustilat olivat siirtyneet luomu- Yleisimpiä rikkakasveja olivat jauhosavikka, pihatäh- viljelyyn vuoden 1994 jälkeen, joten luomutuotannon timö, pillikkeet ja pelto-orvokki. Juolavehnä oli ylei- vaikutus rikkakasvilajistoon ja rikkakasvien runsau- sin rikkaheinä. Kaikkiaan 42 lajia ylitti 10 % ylei- teen oli vasta alkuvaiheessa. Rikkakasvien mekaani- syysrajan. nen torjunta viljakasvustosta oli varsin harvinaista.

242